1. Field of the Invention
The present invention relates to a coupler used for short range non-contact data transmission between two devices located in close proximity to each other, and a communication system including the coupler.
2. Description of the Related Art
In recent years, a variety of proposals have been made and are being put into practice for performing relatively high speed radio communication between two pieces of communication apparatus located in very close proximity to each other at a distance of about several millimeters to several centimeters. For example, it has been proposed to use part of the transmission path connecting between various kinds of information processing apparatus and their peripherals as a radio transmission path. FIG. 28 shows a general configuration for performing communication via the radio transmission path in this case.
As shown in FIG. 28, a first device 10 includes a transmitting/receiving antenna 11, and a second device 20 includes a transmitting/receiving antenna 21, thereby allowing a bus connection between the transmitting/receiving antenna 11 and the transmitting/receiving antenna 12 by radio. Then, the transmitting/receiving antenna 11 and the transmitting/receiving antenna 21 are placed in close proximity to each other at a distance of, for example, several millimeters to perform two-way radio communication.
The communication apparatus shown in FIG. 28 according to the related art is shown in detail in FIG. 29. An antenna communication system 90 shown in FIG. 29 includes the first device 10 having the transmitting/receiving antenna 11, and the second device 20 having the transmitting/receiving antenna 21. The transmitting/receiving antennas 11 and 21 of the respective devices 10 and 20 are placed in close proximity to each other.
The first device 10 includes a data transmitting/receiving section 12, a transmission/reception separating circuit 13, an amplifier 14, a comparator 15, and the transmitting/receiving antenna 11. The transmitting/receiving antenna 11 is connected with the amplifier 14 to which a transmit signal is outputted, and is also connected with the comparator 15 to which a receive signal is inputted. The transmitting/receiving antenna 11 executes radio communication processing with the transmitting/receiving antenna 21 of the second device 20 located adjacent to the transmitting/receiving antenna 11. Transmit data generated in the data transmitting/receiving section 12 is supplied to the amplifier 14 via the transmission/reception separating circuit 13, and amplified in the amplifier 14 for transmission before being transmitted by radio from the transmitting/receiving antenna 11. Also, a signal received by the transmitting/receiving antenna 11 is supplied to the comparator 15, and the level of the receive signal is compared with a threshold. The comparison result is supplied to the data transmitting/receiving section 12 as receive data via the transmission/reception separating circuit 13.
The second device 20 that performs communication with the above-mentioned first device 10 is of the same configuration as the first device 10. That is, the second device 20 includes the transmitting/receiving antenna 21, a data transmitting/receiving section 22, a transmission/reception separating circuit 23, an amplifier 24, and a comparator 25.
FIGS. 23A to 23E are diagrams showing the states of communication processing in the respective devices 10 and 20.
Suppose that, as shown in FIG. 23A, transmit data in which “1”data (high level data) and “0”data (low level data) appear alternately on a bit-by-bit basis is transmitted by radio.
At this time, as indicated by the solid line in FIG. 23B, the output from the antenna on the transmitting side has a signal waveform in which the high level and low level of the transmit data appear as they are. It should be noted that in the case of transmission as differential signals, a signal waveform of inverse characteristic indicated by the broken line in FIG. 23B is also transmitted at the same time.
Upon outputting data from the antenna on the transmitting side in this way, at the antenna on the receiving side placed in close proximity, as shown in FIG. 23C, a derivative waveform is received in which a rate of change in transmit signal appears as a level. For this receive waveform as well, in the case of radio transmission as differential signals, a signal waveform of inverse characteristic is also detected as indicated by the broken line.
This receive waveform is amplified by an amplification function built in the comparator of the receiving system into a signal within a fixed range of level as shown in FIG. 23D, and compared with a threshold on the positive side and a threshold on the negative side. If, as a result of the comparison, the threshold on the positive side is crossed, the signal is held to a “1”data level, and if the threshold on the negative side is crossed, the signal is held to a “0”data level, resulting in the receive data shown in FIG. 23E. This receive data shown in FIG. 23E is the same data as the transmit data shown in FIG. 23A, indicating that radio transmission of the transmit data has been performed correctly.
An example of performing one-to-one high speed non-contact communication between pieces of apparatus located with short range of each other is described in Japanese Unexamined Patent Application No. 2006-186418.